Wednesday, February 26, 2014

Jade Rabbit, "Yutu," the first lunar rover since Lunokhod-2 explored Le Monnier crater for the first half of 1973, in profile, as seen from the Chang'e-3 Panoramic Camera soon after deployment and its first tantalizingly brief trip across a few square meters of Mare Imbrium. The twin dipole antenna extending behind the vehicle are its ground-penetrating array [CAS/CNSA/CLEP].

Paul Spudis

The Once and Future Moon

Smithsonian Air & Space

Another lunar day has come and gone on the barren plains of Mare Imbrium. How fares its most famous terrestrial inhabitant, the Chang’E 3 spacecraft and Jade Rabbit, the little Yutu rover? The fact is, we really don’t know and those that presumably do aren’t talking about it much.

The Yutu rover of the Chang’E 3 mission has experienced some “mechanic control abnormality due to the complicated lunar surface,” is how the Chinese phrased the situation. Details on the nature of the problem are impossible to come by, but one clear result is that the Yutu cannot move. It apparently spent the last lunar day (which lasted from about 10 February until last weekend) sitting in one place. For some scientific investigations, that is not necessarily a problem, but for Yutu’s primary scientific mission, it is fatal.

The goal of placing a rover on the Moon is to explore and examine multiple sites distant from each other. Additionally, the traverse between stations enables unique experiments, such as profiling the surface – the principal objective of the ground-penetrating radar on China’s rover. As the vehicle moves across the lunar surface, it emits radio waves of varying frequency into the surface.

Reflections from subsurface layers or boundaries are then received by the rover’s antenna, thereby allowing scientists to infer subsurface structure. To get a subsurface profile, these measurements must be taken while the rover is moving. Thus, an immobile rover makes this experiment impossible.

The rover’s other instruments operate during a stationary period. However, once a chemical measurement has been made or an image taken, there is little value in continually repeating it.

If the Yutu rover is immobile, its scientific mission is effectively over.

News reports have stopped giving us data and information from the Chang’E 3 lander (which has a camera and an ultraviolet telescope) but assuming it is still operating, it may continue making observations. The lander spacecraft made a panorama of the landing site, so that objective was completed. Presumably, if the UV telescope is still operating, it can continue observing the sky but these observations are not significant to lunar science.

Three LROC NAC views of the Chang'e-3 landing site in north Mare Imbrium (44.1214°N, 340.4884°E, -2630 m elev.), before landing, after deploying the Yutu rover (south of the lander) and after Yutu was moved just to the southeast of the lander, where it apparently failed (and remains) reportedly following a ground-operations error during preparations ahead a long lunar night [NASA/GSFC/Arizona State University].

Thus, from the perspective of lunar science, it appears that the Chang’E 3’s Moon mission is over.

So, how did Yutu do as a lunar explorer? For now, we really don’t know. Aside from a few color images and a chemical spectra that was released to the press, little scientific data has been revealed (a Google translate version of a Chinese web page describing the Chang’E 3 science to date can be read HERE). The data we have seen mostly show that the instruments were functioning. We do not know how many measurements were made, what they have told us, or the geological setting of the chemical analyses.

The Chang’E 3 lander set down very near the rim of a crater 450 meters in diameter, a feature whose walls are littered with angular blocks clearly derived from the local bedrock. The fact that the Yutu did not make an immediate beeline over to those blocks for a detailed examination and chemical analysis tells me one of two things: either those planning the rover’s exploration traverse are not geologists or they didn’t get to it before the rover stopped working.

Yutu has led a famous existence in cyberspace, with numerous “tweets” to the world. A public eager to anthropomorphize machines has responded in kind, including offering several admonitions to the rover to “pay attention to his wake-up calls.” All this rhetorical cuteness hides the fact that China has been less than forthcoming about this mission, as they are about all of their space missions. We hear only what they want us to hear. Successes (of which they have had many) are widely trumpeted with blasts of publicity, while difficulties and failures are buried in silence. It’s true that a space program run by the military (in the case of China, the People’s Liberation Army) will tend toward such an ethic. But the WALL·E-like image promoted by China early in the mission is not the image conveyed by their current posture with the world press.

I find the Chinese attitude both interesting and dismaying. It is similar to one that I experienced with Indian Space Research Organization (ISRO) during the Chandrayaan-1 lunar orbiter mission. When the Chandrayaan spacecraft was running into difficulties after a few months in lunar orbit, the organizational instinct was to deny any problems and be less than forthcoming with the press about the status of the spacecraft.

Spaceflight is inherently difficult and things break all the time. It is beyond ridiculous to cover up a problem by pretending that it doesn’t exist. Similar behavior patterns characterized the early Soviet space program, in which we never heard about mission failures, but successes were given widespread publicity. It seems that to date, China is adhering to that model.

There has been much in the media about the non-welcoming posture of some towards engagement and possible cooperation with China in space – admonishing Congress and NASA to be open to cooperating with China on future space missions. There may come a time when this is possible but for now, it seems that reality is far away.

Dr. Paul D. Spudis is a senior staff scientist at the Lunar and Planetary Institute in Houston. This column was originally published by Smithsonian Air & Space, and his website can be found at www.spudislunarresources.com. The opinions he expressed here are his own, and these are better informed than most.

Tuesday, February 25, 2014

Low reflectance materials splashed out from an unnamed crater, 1260 meter-wide field of view centered on 2.322°S, 81.725°E, incidence angle 3.3° From an Narrow Angle Camera observation swept up over the far western interior of Mare Smythii, LRO orbit 19177, September 12, 2013. LROC NAC M1133662942L[NASA/GSFC/Arizona State University].

Hiroyuki Sato
LROC News System

Today's Featured Image highlights an unnamed fresh crater, about 700 meters in diameter, found on the western edge of Mare Smythii.

The low reflectance materials extend out in an distinctive bell shaped pattern from the southwestern edge of the crater rim. The interior crater wall near this deposit also shows splashes of relatively darker materials, as well as three other dark patches (at 12, 2, and 5 o'clock, relative to the crater center).

These deposits are likely similar in nature to the excavated dark deposits emplaced near the rim, and they appear to have partially flowed back into the cavity.

Enigmatic low reflectance material and surroundings in the context of the full 7.2 km width of LROC NAC observation M1133662942L [NASA/GSFC/Arizona State University].

Normally, ejecta travels radially from the impact center, resulting in lineations in the ejecta or rays pointing away from the source crater. In this bell shaped deposit, however, the two main dark lines outlining the bell are curved and extend about 150-200 m outside of the rim. Note that the surrounding terrain of this unnamed crater is nearly flat (see next WAC context); there are no readily apparent obstacles that might have affected the ejecta trajectory. Perhaps the original low reflectance deposits were unevenly buried, resulting in the curved dark patterns after excavation and final emplacement. What is the darker material? Since the crater is near the highland / mare boundary we might be seeing dark basalts or pyroclastics mixed with bright anorthositic crust.

Friday, February 21, 2014

The central peak of Icarus crater rising out of the shadows to greet a new lunar day! Image field of view approximately 10 km (north is at right. LROC NAC oblique mosaic M1124685518LR, LRO orbit 17914, June 1, 2013; spacecraft and camera slew 62.84° from nadir, resolution 3.3 meters per pixel and captured from 106.53 km over 5.58°S, 193.85°E [NASA/GSFC/Arizona State University].

H. Meyer
LROC News System

Icarus crater is one of a kind on the Moon; its central peak rises higher than about half its rim. Most central peaks rise only about halfway to the crater rim. Icarus' large, rounded central peak resembles that of Alpetragius on the eastern limb of Mare Nubium.

The disproportionate size of the central peak may be because both Icarus and Alpetragius are close in diameter to the transition between central peaks and peak rings.

A reduced resolution image of the full NAC oblique looking from east to west across Icarus crater (5.348°S, 186.579°E). Notice the gentle slopes of the terraces on the crater wall and many superposed craters that suggest that Icarus is quite old. Icarus is approximately 94 km in diameter . LROC NAC oblique mosaic M1124685518LR[NASA/GSFC/Arizona State University].

Icarus is located just west of Korolev crater on the lunar farside. Like the floor of Korolev, the floor of Icarus is covered with relatively smooth light plains material that can be seen outside the crater as well, filling not only crater floors but also the surface between craters in the highlands (See WAC context image below).

LRO WAC image of Icarus crater and vicinity (5.49°S, 186.74°E) in the lunar highlands. Image field of view approximately 365 km, Korolev crater and the Orientale basin are both east of this site [NASA/GSFC/Arizona State University].

These light plains were deposited during the formation of the Orientale basin, which is located over 1500 km away! The specific mechanism by which the light plains were emplaced is still under investigation, but the plains are likely made of ejecta produced during the formation of the Orientale basin.

A reduced resolution version of the full NAC oblique of Hayn crater (64.58°N, 83.89°E). Hayn is approximately 86 km in diameter. North at right; LROC Narrow Angle Camera oblique mosaic M1105158497LR, orbit 15170, October 18, 2012; incidence angle 78.44° at a roughly estimated resolution of 4.7 meters per pixel. Spacecraft and camera slewed 57.46° west of nadir, from 179.93 km over 68.01°N, 111.56°E [NASA/GSFC/Arizona State university].

In the full oblique image above, the walls of Hayn display large terraces that formed in the final stage of crater formation, called the modification stage. They are the surface expression of concentric listric faults.

Another, perhaps superfluous though certainly extraordinary, contexual view of Hayn with its emphasis on the crater's proximity with the Moon's north pole. LRO LOLA false color laser altimetry, at 128 points per pixel, through NASA's ILIADS application, a false perspective from 447 km over 55.3189°N, 78.7145°E, a point measured 4.127 km below mean global elevation (The image can be seen at its full size by clicking on it or HERE.) [NASA/GSFC/MSFC].

LRO WAC image for context. Orthographic projection, field of view is approximately 220 km across [NASA/GSFC/Arizona State University].

These faults develop as the transient cavity undergoes gravitational collapse. The formation of terraces widens the crater cavity and shallows out the floor. This downward movement of the walls and floor is followed by uplift in the center as the crust accommodates the stress of the impact.

Friday, February 14, 2014

Series of LADEE star tracker images show the starfield against which the spacecraft baselines the data it collects eclipsed by the Moon below, as the short-lived mission's orbit skirts the northern edge of the Aristarchus plateau [NASA/ARC].

Rachel Hoover
NASA Ames Research Center

Earlier this month, NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) observatory successfully downlinked images of the moon and stars taken by onboard camera systems, known as star trackers. This is the first time the LADEE team commanded the spacecraft to send these pictures back to Earth.

The main job of a star tracker is to snap images of the surrounding star field so that the spacecraft can internally calculate its orientation in space. It completes this task many times per minute. The accuracy of each of LADEE's instruments' measurements depends on the star tracker calculating the precise orientation of the spacecraft.

"Star tracker cameras are actually not very good at taking ordinary images," said Butler Hine LADEE project manager at NASA's Ames Research Center in Moffett Field, California "But they can sometimes provide exciting glimpses of the lunar terrain."

Given the critical nature of its assignment, a star tracker doesn't use ordinary cameras. Star trackers' lenses have a wide-angle field of view in order to capture the night sky in a single frame.

The images shown here were acquired on February 8, 2014, around 2345 UT, while LADEE was carrying out atmospheric measurements. The series of five images were taken at one-minute intervals, and caught features in the northwestern hemisphere of the moon. LADEE was traveling approximately 100 km per minute along its retrograde semi-equatorial orbit. All images were taken during lunar night, but with Earthshine illuminating the surface.

The initial image captured the smooth-floored crater Krieger (22.86 km, 29.02°N, 314.39°E) on the horizon, with 7 km Toscanelli in the foreground.

The second image shows Wollaston P, about 4 km across near the horizon, and the southeastern flank of the lunar mountain Mons Herodotus.

The third image caught a minor lunar mountain range Montes Agricola, the northwest frontier of the Aristarchus Plateau, as well as the flat-floored crater Raman, about 10 km in diameter.

Location of LADEE Star Tracker Cameras in relation to its primary components [NASA/LEAG].

The star trackers will operate while LADEE continues to measure the chemical composition of the atmosphere, collect and analyze samples of lunar dust particles in the atmosphere and hope to address a long-standing question: Was lunar dust, electrically charged by sunlight, responsible for the pre-sunrise glow above the lunar horizon observed during several Apollo missions? And who knows? The star trackers may help answer that question.

Thursday, February 13, 2014

Fractured crater draped with ejecta from the impact event that created the Orientale basin, south of Buffon crater (downslope to the right). Crop from LROC NAC oblique mosaic M1128039712LR, LRO orbit 18386, July 9, 2013; 74.2° angle of incidence, resolution very roughly 2.3 meters, spacecraft and camera slewed 65.27° toward the east, from 58.43 km over 46°S, 222.48°E [NASA/GSFC/Arizona State University].

J. Stopar
LROC News System

This spectacular oblique view looks from west to east across an area south of Buffon crater (45.715°S, 229.052°E) that is draped with impact ejecta from the Orientale Basin.

Orientale ejecta to have flowed over a pair of modified craters (each approximately 16 km in diameter, also see image at far bottom). Because the ejecta is superposed on top of the craters and appears to flow over much of the scene, the ejecta should be younger than the craters. However, these craters do not exhibit typical morphologies, and neither does the Orientale ejecta! Just how did this spectacular scene form?

Full width NAC oblique image of Orientale ejecta covering the local terrain. Ejecta and crater floors are lumpy and crisscrossed by numerous graben. A flat lying mare pond is located just below center on the right side of the image (arrow). Scene is approximately 41 km in height, oblique view, west to east. Click image or HERE to view larger image [NASA/GSFC/Arizona State University].

First, the pair of prominent craters seen above have concentric, mounded or lumpy looking floors. This morphology is atypical of impact craters of this size (see Steno Q or Burg crater for more typical examples), but is reminiscent of many floor-fractured craters (such as Atlas or Komarov), which are thought to form through uplift caused by magma intruding deep beneath the surface. However, the graben seen in the examples above are more subdued those in most floor-fractured craters, suggesting that they may be blanketed by the overlying Orientale ejecta.

There is also a small pond of basalt (darker and flat) exposed just below the center on the right side of the full width image (above). This is a tell-tale sign of volcanic activity in the area, lending support to the hypothesis that the lumpy craters were modified by magma from below. This, however, does not prove which occurred first: the volcanism or the emplacement of the Orientale ejecta.

LROC Wide Angle Camera (WAC) mosaic of the area south of Buffon crater. Blue polygon highlights approximate boundaries of the area shown in the featured oblique Narrow Angle Camera (NAC) frame; arrow indicates location of impact melt flow featured in a previous post. The ejecta within the blue polygon is fractured and warped, but the ejecta indicated by the arrow is not [NASA/GSFC/Arizona State University].

The final observation that informs the sequence of events is the occurrence of similar graben in both the crater floors and the adjacent ejecta outside the craters that is not typical of Orientale ejecta in this region. The previous post Stopped in its Tracks featured a nearby Orientale ejecta deposit located only 30 kilometers west of today's spectacular image; that ejecta is not crisscrossed by graben like those seen in the opening image above! Thus, volcanic activity in this area may have occurred after the large impact event that formed the Orientale basin around 3.8 billion years ago. However, further analysis and age dating in this area are needed before we can say for certain that the Orientale ejecta was modified (or overprinted) by younger volcanism.

Special Session on Lunar Dust and Exosphere Featuring the First Results from LADEE: This session will address new results concerning the lunar exosphere, the mystery of electrostatically lofted dust, and other new research concerning the exotic phenomena surrounding the nearest example of a surface boundary exosphere. The focus will be on results from the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission, but will also incorporate relevant Lunar Reconnaissance Orbiter (LRO) exosphere/dust measurements and ARTEMIS observations related to LADEE science.

LADEE is making measurements of the tenuous lunar exosphere and the dust cloud from meteoroid impacts. The talks presented in this special session will highlight LADEE’s preliminary science results. These include initial observations of argon, neon and helium exospheres, and their diurnal variations; the lunar micrometeoroid impact ejecta cloud and its variations; spatial and temporal variations of the sodium exosphere; and observations of sunlight extinction caused by dust, as well as other topics.

The LADEE search for a dust exosphere is discussed in the context of recent dust upper-limit measurements. In general the detection of a small-grain dust population consistent with the low Clementine and LAMP upper limit estimates will be a challenge for the LADEE mission. On the other hand, these prior measurements represent only a small part of the LADEE search space, and none coincide with the occurance of major meteor streams. The LADEE dust search is sure to produce surprises.

9:00 a.m. Horanyi, Gagnard, Gathright, Gruen and James, et al. - The Dust Environment of the Moon as Seen by the Lunar Dust Experiment (LDEX), #1303

The Lunar Dust Experiment (LDEX) onboard the LADEE mission continues to make observations in lunar orbit since its cover was deployed on October 13, 2013.

Figure 2. Summary of LADEE/LDEX activities through January 3, 2014. The number of recorded events (noise and dust impacts) sharply increased following LADEE orbit lowering maneuvers. An unusually large burst of events was observed November 12, most likely related to the Taurids meteor stream, and the following intense period, starting December 13, coinciding with the Geminids and the landing of Chang’e-3.

This talk will report about first insights into the properties of the lunar dust exosphere based on a preliminary analysis of the LDEX data. The transmitted data set is already larger than any other existing observation of a dust exosphere by orders of magnitudes and deepened our insight into the physics of this important phenomenon. This talk will report about first insights into the properties of the Lunar dust exosphere based on a preliminary analysis of the LDEX data.

We describe the 18 annual meteoroid streams predicted to encounter the Moon during the LADEE mission, and discuss the implications for the lunar environment.

Figure 1. Locations of radiants for 18 annual meteor streams at the time of peak activity plotted as Selenographic Solar Ecliptic (SSE) latitude and local time. The points are color-coded to show the Zenith Hourly Rate (ZHR) at the peak in shower activity. (ZHR is the hourly rate of meteors seen by standard a observer on the Earth under optimum viewing conditions.) For our purposes ZHR serves as rough guide to meteoroid flux rates incident at the Moon. Only six of the 18 streams have peak ZHR exceeding background HR so it is reasonable to assume these streams will likely have the most noticeable effects on the lunar environment compared with typical conditions. (Gray shading covers the latitudinal range of the LADEE orbit.)

Relative positions of the LADEE with the ARTEMIS P1 and P2 spacecraft early on December 23, 2013 [NASA/JPL-CalTech].

The goal of the LADEE mission is to understand the exosphere of the Moon, including its structure, temporal variability, and sources and sinks. To achieve this goal, we must determine how exospheric dust and neutrals behave, not in isolation, but as part of an inextricably coupled system that includes the surface and the plasma environment.

A schematic of the very dynamic lunar ionosphere put together originally by Jasper Halekas, now an investigator with the ARTEMIS program.

Charged particles, their interactions with the surface, and the electric and magnetic fields that they produce and respond to, contribute to source and sink processes for both lofted dust and exospheric gases, and therefore to their spatial and temporal structure and variability. The LADEE payload does not include plasma instrumentation; instead, we utilize a combination of ARTEMIS measurements of upstream plasma parameters and data-based modeling to determine plasma quantities around the Moon, including at the LADEE orbit and in the regions covered by UVS scans and those providing the source populations ultimately measured by LDEX and NMS.

The ARTEMIS (Acceleration, Reconnection, Turbulence, & Electrodynamics of Moon’s Interaction with the Sun) mission consists of two probes from the heliospheric constellation THEMIS retasked to the Moon in 2011. ARTEMIS provides comprehensive measurements of charged particles and magnetic and electric fields around the Moon from a two-point vantage that enables continuous upstream plasma monitoring.

Early representation from the highly innovative proposal to gradually reposition two of the five member constellation of THEMIS probes into lunar orbit, where today they operate as ARTEMIS P1 and P2. On the way to being re-tasked, the vehicles became the first to orbit the Earth Moon Lagrange points L1 and L2. Their functions are presently an important part of the LADEE mission.

The two ARTEMIS probes currently reside in stable near-equatorial elliptical orbits. An orbital design targeting periapses near the lunar dawn terminator.

The ambient plasma, directly and through its control of the nearsurface electrostatic environment, contributes significantly to the exospheric cycle. By comparing various measurements, and utilizing ARTEMIS-measured fields to determine their trajectories and likely sources, we can obtain additional constraints on the sources, composition, and dynamics of the tenuous lunar atmosphere..

ARTEMIS provides a variety of plasma measurements which show a high degree of correlation with LDEX current measurements. There are two regions in the LDEX data that show consistent correlation: 1) the subsolar point and 2) the time LADEE crosses into umbral shadow.

Shown in Figure 3 are the average LDEX current for 15 minutes from subsolar and shadow crossing time respectively. Additionally, the component of the convection electric field parallel to the LDEX boresight appears to be significant in LDEX’s current measurements and will be discussed in this presentation.

This talk will focus on the correlations between LDEX and ARTEMIS data.

Figure 2. - LDEX current measurements. Above: Orbit with high LDEX current variability, and bottom: Quiet period in LDEX current data.

The lunar exosphere is a tenuous, collisionless combination of various neutral species derived from a variety of sources, including charged particle sputtering, micrometeoroid impact vaporization, internal gas release, and photon-, electron-, and thermally-stimulated desorption. Solar irradiation will photoionize these neutrals which are in turn picked up by the ambient interplanetary magnetic and electric fields and lost to interplanetary space.

The Lunar Dust EXperiment (LDEX) onboard the Lunar Atmospheric and Dust Environment Explorer (LADEE) is currently searching for the signature of charged, sub-micron sized dust grains lofted to kilometer altitudes above the lunar surface, but such measurements are also sensitive to ambient, low-energy ions including those of lunar exospheric origin.

The LADEE Lunar Dust Experiment (LDEX)

We model the response of the LADEE/LDEX instrument to low-energy lunar dayside ions and discuss implications for the lunar exosphere and ionosphere.

We present early observations of He, Ar, and Ne observations from the LADEE NMS in lunar orbit. The Neutral Mass Spectrometer (NMS) of the Lunar Atmosphere and Dust Environment Explorer (LADEE) Mission is designed to meas-ure the composition and variability of the tenuous lunar atmosphere. The NMS complements two other instru-ments on the LADEE spacecraft designed to secure spectroscopic measurements of lunar composition and in situ measurement of lunar dust over the course of a 100-day mission in order to sample multiple lunation periods.

Instrument activities are designed and scheduled to provide time resolved measurements of Helium and Argon and determine abundance or upper limits for many other species either sputtered or thermally evolved from the lunar surface.

Figure 3. Evolution of Helium abundance (in instrument counting units) as a function of solar local time observed during the LADEE commissioning phase.

Early Results From NMS Observations: Owing to its very low chemical background the NMS instrument was successful at detecting and mapping exospheric Helium during the high altitude (250 km) commissioning phase. This early mapping campaign provided the unique opportunity to observe variation of Helium at a constant altitude, for nearly a full lunation. Figure 3 shows results of Helium spatial and temporal variability as the Moon moves in and out of the Earth’s magnetotail.

LADEE Neutral Mass Spectrometer (NMS)

At the end of the commissioning phase and after the orbit’s periselene was lowered to approximately 50 km, the NMS was able to detect Argon and Neon.

This talk will overview the design, performance, and initial results of the LADEE UVS instrument.

UVS deployed its limb-viewing telescope door on October 17 and began a series commissioning activities, including pointing, wavelength and preliminary radiometric calibrations. UVS made its first lunar limb observations on October 23, 2013.

UVS has been routinely monitoring two previously measured atmospheric species, potassium and sodium, and has been making observations to search for other, previously sought species including OH, H2O, Si, Al, Mg, Ca, Ti, and Fe. UVS is also able to detect the scattered light from lofted dust between the altitudes of a few km up to 50 km using its limb telescope, as well as search for dust very near the surface using solar occultation measurements. The UVS instrument operates between 230 – 810 nm with a spectral resolution of less than 1 nm. The spectrometer has been operating nominally.

LADEE ultra-violet - visible light (UVVIS) spectrometer (UVS)

Limb observations, using the UVS three-inch telescope, have been made on a routine basis, with limb “stares” at 20 km at the terminators, and 40 km at around local noon time. At the terminators the spacecraft “nods” the telescope between the surface and about 50 km. At noon it was found that near-surface scatter precluded observations below about 30 km, so nods are not performed then. There have been a mix of both “backward” looks (stares that point in the anti-velocity direction of the spacecraft), and “forward” looks (which flip the spacecraft to allow UVS to look in the velocity direction). This permits observations both in and away from the direction of the sun.

LPSC-2014, #2518 - Figure 1. Schematic of a LADEE “nod” operation to detect dust and gases at the lunar limb with the UVS. Nod begins in the stare orientation, scans down to lunar surface, up to higher altitudes, then back to stare. This activity provides science data at many altitudes down to lunar surface. The telescope can also be pointed 180° opposite from normal Limb stare orientation to allow for observations in forward scatter at sunset terminator.

Occultations have been performed about once every two days, tracking the sun as it sets behind the sunrise terminator between about 35 km and the surface. In this mode UVS has gathered spectra at a rate of either 15 msec or 26 msec, corresponding to a spatial sampling of less than 1 km with very high SNR (typically less than 500 for a single scan).

Sodium and potassium are regularly measured in all activities, except for occultations. Trends in these measurements are made both spatially and temporally, and associations are with specific events, such as meteor streams, and surface composition are examined.

This study presents preliminary results of lunar limb observations from the UVS on LADEE toward understanding the impact contribution to the dust exosphere.

“Larger” impact events (e.g., impactor size>>target grain size), which are expected to form sporadically over the course of a year, are capable of lofting a considerable amount of material for a measureable period of time. As these ejecta return to the surface (or encounter local topography), they impact at hundreds of meters per second or higher, thereby “scouring” the surface with low-mass oblique dust impacts. While these high-speed ejecta represent only a small fraction of the total ejected mass, the lofting and subsequent ballistic return of this dust has a high potential for mobilization.

The actual visibility of these ejecta clouds diminishes with height and time as the particles spread ballistically.

Given the amount of material expected to be lofted above 5km, these results indicate that there is a significant chance of LADEE observations of a primary ejecta cloud even from relatively small impacts- if they occur at the right time and place (e.g., at a location and recently enough to enter the fields of view of the instruments before spreading too much).

The chances of observing such an event grow significantly higher during a meteor shower, which have been observed to cause very frequent impact flashes on the moon. around the moon for durations of several hours. These smaller, more frequent, craters can loft diminished (but measurable with the UVS & LDEX instruments) amounts of regolith for tens of minutes.

Figure 1. (a) UVS solar viewer foreoptics, showing six sequential baffles, which define the field of view and minimize the contribution from off-axis scattered light. The solar diffuser is shown just before the fiber optic input, which leads to the spectrometer. (b) Schematic of an UVS occultation session showing the solar viewer field of view cone, grazing the lunar exosphere and subsequently the lunar limb, as LADEE’s orbit progresses through local sunrise.

Figure 2. A light curve from an example occultation activity, annotated with cartoons of the Sun as seen from the UVS solar viewer. The yellow line around the Sun in each cartoon marks the solar viewer field of view. Each view corresponds to a different section of the solar occultation light curve.

Our preliminary results indicate wavelength dependent extinction as a function of altitude. We attribute the detected spectral color changes to the presence of sub-micron sized dust grains in the lunar exosphere. Details of these results will be presented, and compared to previous models of the lunar dust exosphere.

The native lunar exosphere is sparse. The estimated total mass of the lunar exosphere is ~107 g, with a source rate of ~10 g/s. Landing a vehicle such as the Chinese Chang’e-3 lander on the surface of the Moon would require burning an estimated 106 g of rocket fuel over ~12 minutes.

Thus, the introduction of vapor into the lunar environment via rocket exhaust during a soft lunar landing constitutes a 100 times temporary enhancement to the source rate to the lunar exosphere and an increase in the total mass of 10%. Whereas the native lunar exosphere is comprised primarily of helium and argon; the rocket exhaust comprises water, carbon dioxide, ammonia, and other HCNO products.

The distribution of particles in the lunar exosphere is largely controlled by the interactions between the particles and the lunar surface. For example, helium does not stick to lunar regolith grains, thus follows an inverse relationship between the density and the surface temperature. In contrast, argon does stick to the surface at colder, nightside temperatures. Argon density is observed to peak at the terminators.

Thus, if the propagation of the exhaust vapors can be monitored, it can reveal previously unknown properties of the gas-surface interaction with the lunar regolith. We model the release and propagation of the exhaust gases on the Moon and compare to observations in orbit around the Moon from the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft.

View of the Moon at gamma-ray wavelengths, as imaged by the Compton Gamma Ray Observatory satellite. These gamma rays are induced by the collision of cosmic rays with the lunar surface, the same process recently found able to synthesize organic molecules in lunar polar ice deposits [Dave Thompson (NASA/GSFC) et al., EGRET, Compton Observatory].

Paul Spudis

The Once and Future Moon

Smithsonian Air & Space

A recent study indicates that water ice and simple molecules of carbon and nitrogen might form the seed material for more complex substances, some of which might ultimately be involved in the origin of life. The work from the University of Hawaii took measurements of the levels of cosmic radiation from the Lunar Reconnaissance Orbiter (LRO) and applied it to a composition similar to that observed by the impacting LCROSS probe at the south pole of the Moon.

As you may recall, this probe found both water vapor and ice particles ejected by the impact in one of the permanently dark regions near the pole; it also observed additional compounds, including methane, ammonia and some other simple organic molecules. These substances are present in cometary ices and thus, it was thought that their presence could indicate a cometary origin for the Moon’s polar ice.

The new work does not negate that interpretation, but adds complexity to the puzzle by showing that it may be possible to manufacture some of the more complex organic molecules from the simple substances found in cosmic ice, whether deposited from the nuclei of impacting comets or made in place within the cold traps of the lunar poles. Once again, we find that the polar regions of the Moon are even more interesting scientifically than we had thought.

The generation of new and more complex organic compounds must be a surficial process since material buried at levels deeper than a couple of meters is shielded from even the most energetic cosmic rays. For this reason, the material observed during the LCROSS impact is likely of cometary origin because most of the ejecta created by that impact comes from depths of a few meters. While material in the lunar surface is overturned by impact gardening, such overturn is extremely slow (rates of overturn below about 1 meter depth occur on timescales of greater than 1 billion years, the same timescale on which this radiation-induced production occurs).

The generation of complex organic molecules is an important topic of research for the origin of life. Most scientific strategies focus on the search for extraterrestrial life in more Earth-like environments, such as a previously warmer and wetter Mars or in the hypothesized deep oceans of Europa. A few studies have focused on the physical processes of organic chemistry, specifically the generation of complex molecules in space, within small bodies such as cometary nuclei and on primitive planetary surfaces, such as the polar deposits of the Moon and Mercury. Findings to date show that complex organic substances are generated in a variety of environments and under a variety of energetic conditions.

Because they date from early in Solar System history and contain the materials needed for living systems (water and organic matter), comets have long been thought to be the seedbeds of life. Comets are remnants of the original solar nebula, the cloud of debris out of which our Solar System formed. At a certain position and beyond in the nebula, water is stable in solid form (the so-called “frost line”); in our Solar System, the frost line is between the orbits of Jupiter and Mars. Water in nebular material inside this line vaporized and was dissipated by the solar wind, some blown outward and some disassociated by ultraviolet radiation. But water outside of the frost line can condense into ice particles, which then may be accreted into planetary objects. The smallest and most water-rich of these objects are the comets, most of which originate far beyond the frost line in the most distant regions of our Solar System (the so-called “Oort cloud”). Larger icy objects in the outer Solar System include the satellites of the Jovian planets, which are predominantly made of water ice with minor amounts of admixed rocky material. The inner (terrestrial) planets such as Earth and Mars are made mostly of rocky material but contain minor amounts of water, a consequence of their incorporation of cometary material during assembly and subsequent impact bombardment.

This last process operates on the Moon as well. Because the Moon represents a stable, unchanging environment over billions of years, it accumulates the evidence and detritus of the impact history of that era. Most of the volatile component of this impacting debris is lost from the Moon, but any of it that becomes trapped in the cold, dark areas near the poles remains there forever. The poles of the Moon are thus a natural laboratory for the study of one of the early processes in Solar System history – the creation of complex organic substances from the more primitive and simple elements and compounds. In this sense, the pre-biotic organic chemistry of the lifeless and barren Moon serves the cause of the study of life’s processes and origin.

As we continue to study the Moon, we find that it offers much more than one might suspect at first glance. The Moon’s early history reveals the secrets of planetary assembly, impact bombardment, global melting and differentiation into core, mantle and crust. Its middle history tells us about the thermal evolution of planets, as internal heat spawned the volcanism that resurfaced part of the Moon and operates on all of the terrestrial planets. The continued impact history recorded in the Moon’s surface layer documents a phase of Earth history missing from our terrestrial geological record, including the possibility of episodic waves of impacts that are at least partly responsible for extinctions of life recorded in the fossil record. This same surficial layer also records the history and output of our Sun, the provider of energy to the planets and the principal driver of climate change on Earth. The interconnections between the various branches of lunar science with the other sciences grow more evident and more significant over time.

This new research makes the recently renewed interest in the value of the Moon and new lunar missions more comprehensible. Far from being a mere echo of some previous space glory, a return to the Moon to undertake new scientific studies, new exploration and to develop a wholly new set of technologies impacts all of space science and exploration in many different and unexpected ways. Insights into the origins of life can come from detailed examination of lunar polar volatiles. These same materials can also enable travel to more distant destinations and open up Earth-Moon space to economic development. In both cases, lunar return will enable and facilitate our understanding and movement into space.

As my colleague David Lawrence of APL put it, “One of the take-homes is, go back to the moon and look. Dig up samples, see what’s there.” Sound advice.

Profile of Yutu, the first lunar rover since 1976, from the Chang'e-3 Panoramic Camera, from an image sequence released January 17. Click on image or here for larger view [CNSA/CLEP/CAS].

Never officially confirmed (or denied), reports that China's solar-powered lunar rover Yutu (Jade Rabbit) did not survive a second 14 day-long, bitterly cold lunar night have proven to have been premature. Late Wednesday, Beijing time, as the Sun rose higher over the Mare Imbrium landing site, the rover was almost fully revived.

"Our rabbit is awake," reported Yong-Chun Zheng of the Chinese Academy of Sciences. "Instruments on the rover stood up to the challenge of the very low temperatures during the lunar night."

Followers in social media communities, both on and off the mainland, were expressing condolences over the loss of the wheeled vehicle. As dawn occurred at the landing site, February 9, while no official announcement as to the rover's fate has been released.

The rover's solar panels apparently did not retract before the beginning of its second
night on the Moon in late January. The vehicle was believed to be almost
certainly lost from that point, as state media reported. The panels were designed to be integral thermal protection for sensitive control circuitry.

The Chang'e-3 lunar lander, on the other hand, had successfully hibernated through its second night and been revived while the rover it had deployed soon after landing on the Moon in December was unsuccessfully buttoned-up for a second night on the lunar surface.

Scientists had feared the worst for the small rover, and awaited official announcement.Congratulatory messages from throughout the world arrived as news spread that engineers had successfully transmitted and received a signal from Yutu.

"The rover can receive commands from the ground," Zheng wrote, "and we have received data from the rover."

The extent of any long-term damage and whether efforts to properly place the rover into hibernation ahead its third lunar night will be successful are still unclear. Zheng reported, however, ground engineers are optimistic that the rover will return useful science.

"Except some sensitive components, most of the functions of the rover have been recovered, Zheng wrote. "Our experiences will contribute to future lunar missions, both with the lander and rover. Lunar and planetary missions are never easy, always sources of joy mingled with surprise, but we anticipate the brave Jade Rabbit will yet gain new discoveries on the Moon."

Yutu is the first remote-operated lunar rover successfully operated on the Moon since the Soviet Union's Lunokhod-2 in 1976.

The planetary science community throughout the world have hailed the Yutu rover's deployment from the Chang'e-3 lander, quick to point to initial science results and operations following even a single lunar night as reasons to call the still-ongoing Chang'e-3 and Yutu missions successful.